The present invention relates to a bone cement. More particularly, the present invention relates to a bone cement wherein a diagnostic or therapeutic agent is incorporated in the liquid component with the agent being incorporated by the use of an emulsifying agent.
Bone cements find wide usage in a variety of applications. For instance, they are used for cementing implants in place, for the anchoring of endoprostheses of the joints, in the treatment of skull defects, and for the performance of spinal fusion.
Typically, these bone cements are made by mixing together a powdered homopolymer or copolymer of methylmethacrylate and a suitable liquid monomer, usually methylmethacrylate in the presence of a catalyst system. Additionally, the bone cement may also contain x-ray contrast agents, such as barium sulfate or zirconium dioxide, or dyes for the identification of the bone cement in the body.
In usage, a doughy mixture is prepared from the two components which is then placed in the body and allowed to set in situ due to polymerization of the monomer. Polymerization of the monomer can be accelerated by the presence of a redox catalyst system, usually an organic peroxy compound, such as dibenzoyl peroxide, plus a reducing component, such as p-toluidine.
The placement of a foreign object, such as the bone cement or cemented prosthesis, requires that prophylactic measures be taken to guard against infection at the boundary surfaces found between the bone cement and bone, and/or between the bone, bone cement, and prosthesis. Such prophylactic measures have generally involved the addition of antibiotics to the bone cement.
For instance, in U.S. Pat. No. 4,059,684, the antibiotics which are added to the bone cement are the hydrohalides or sulfates of gentamicin in combination with sodium chloride, potassium chloride, sodium bromide or potassium bromide. In this patent, the antibiotic can be incorporated into either the powdered polymer or copolymer or the liquid monomer. No mention is made of the addition of an emulsifying agent to incorporate the antibiotic into the liquid monomer.
Other antibiotics which have been added to bone cement include penicillin and tetracycline, which in most instances, are added to the powdered polymer or copolymer.
In United Kingdom Patent No. 1,532,318, the methylmethacrylate liquid monomer is present as an emulsion in water. No mention is made of the incorporation of antibiotics into this monomer.
In all situations wherein an antibiotic is added to a bone cement, the initial release is in a relatively high concentration to assure its bactericidal and bacteriostatic action. After this initial release, a diminution of the concentration takes place with the release rate, which is now lower, remaining relatively constant over a longer period of time. The net result is that even though the antibiotic release is sustained, the active concentration of the antibiotic is low. Thus, early infections may be prevented but later infections may not be reliably prevented or combatted. As is known, increasing the concentration of antibiotic may impair the mechanical strength of the bone cement so there remains a need for a bone cement from which the antibiotic will be released at both a sustained rate and at a high concentration.